1. Field of the Invention
The present invention relates to a method and apparatus for controlling the movement of an optical pickup in an optical disc player, more particularly, a method and apparatus for adjusting the driving signal, which is to be supplied to a sled motor, to move an optical pickup between tracks radially in an optical disc player.
2. Description of the Related Art
Referring to FIG. 1, a general optical disc player that reproduces optical discs in which MPEG-encoded digital data are stored comprises a pickup 3 for reading out information recorded in an optical disc 1 by using a light beam irradiated by its LED (laser emitting diode); a sled motor 4 for moving the pickup in the radial direction of the optical disc 1; a spindle motor 2 for rotating the optical disc 1; a driving unit 6 for driving the sled motor 4 and the spindle motor 2; a RF (radio-frequency) amplifier 5 for amplifying a signal picked up by the pickup 3; a servo unit 7 for servo-controlling the driving unit 6 based on focus error signal, tracking error signal, and the rotational speed of the optical disc 1 and extracting synchronization signal from the output signal of the RF amplifier 5; a DSP (digital signal processor) 8 for filtering the signal from the RF amplifier 5 and for demodulating the filtered signal; an MPEG decoder 8 for decoding the demodulated data from the DSP unit 8; a MICOM (microcomputer) 11 for controlling the data flow between the above-mentioned components; and a memory 12 for temporarily storing the decoded digital data.
In an optical disc player configured as shown in FIG. 1, details of track jump operation are as follows. To move pickup 3 from a present track to a target track in response to a search mode command entered into the MICOM 11, the MICOM 11 obtains positional information on a present track position at which the pickup 3 is located from reproduction control data which is provided from the DSP 8. And then, the MICOM 11 calculates the current track number of the pickup 3 by using the positional information. The positional information of the pickup 3 is represented by MSB (minute/second/block) date where the optical disk 1 is a CD (compact disc). In case of a digital video disc (DVD), the positional information is represented by the track number. The number of tracks for the pickup 3 to traverse and the direction (toward the inner circumference or the outer circumference) are obtained by subtracting the current track number from the target track number.
By multiplying the number of tracks to traverse by the standard track pitch, the MICOM 11 calculates the moving distance of the pickup 3 to the target track. The MICOM 11 controls the driving unit 6 through the servo unit 7 in order that the driving unit 6 supplies a driving signal to the sled motor 4. The sled motor 4 rotates for a period of time in which the driving signal is applied so that the pickup 3 is moved to the target track.
After the pickup 3 is moved for the aimed distance, the present location of the pickup 3 is read out again from the optical disc 1 to determine if the pickup 3 is located at the target track. If the location is not the target track, the pickup is further moved until the pickup is located at the target track. That is, fine search process is performed to complete the track jump operation.
Therefore, when a long jump operation between tracks is performed, the pickup 3 is positioned at the target track as close as possible in order to shorten the time for the fine search operation and thereby achieve high-speed access.
FIG. 2 is a flow chart according to the conventional art method for controlling the movement of an optical pickup in an optical disc player, which will be described now in detail. If there is a request to move the pickup for the same distance as that of previous movements (S11), an adjustment operation in which a driving pulse for driving the sled motor is performed for a predetermined number of times. To be specific, first, the pickup 3 is moved to a target track by supplying a driving pulse to the sled motor 4 (S12). A sub-Q code, which contains the information regarding the current location of the pickup 3, is read from the track at which the pickup 3 is currently located and is then used to calculate a track error signal (S13). If there is any track error (S14), the shape of the sled motor driving pulse (kick pulse) is changed with accordance with the track error signal (S15). Next, the number of iterations is checked to determine whether to terminate this operation (S16). If it is less than the predetermined number of times ("N"), the pickup 3 is moved back to the initial track and then the process of steps S12 to S16 is repeated with the adjusted driving pulse.
In short, in the conventional art method, the sled motor driving pulse signal is adjusted repeatedly in such a manner that the pickup 3 is moved to the target track as precisely as possible, or the track error is minimized each time the pickup is moved from the current track to the target track. Peak level or width of the sled motor driving pulse is adjusted to compensate for the feedback track error, as shown in FIGS. 3A and 3B.
However, the movement of the pickup according to the conventional art method may not be accurate for distances other than the moving distance used in the iterative adjustment of the sled motor driving pulse. The conventional art method is, moreover, used only when an optical disc is loaded in optical disc players because it needs to read sub-Q code from the optical disc in order to be aware of the current location of the pickup.
The conventional art method for controlling the movement of the pick does not deal with deviations in access time across optical disc players by slight deviation between optical disc players. That is, due to frictional resistance between the sled rail and the sled motor and mass thereof, the load applied to the sled motor shaft is different from one player to another, resulting in great delay to access target data tract in a certain optical disc player.